The present invention relates to a fault diagnosis system for a rotor winding of a rotary electric machine such as a large-capacity turbine generator, or more in particular to a rotor winding fault diagnosis system suitable for detecting inter-layer shorting of the rotor winding.
Conventional rotor winding fault diagnosis systems of this type generally used in the past, as one of such examples is disclosed in U.S. Pat. No. 4,377,784 or JP-A-58-12555, comprises a magnetic flux detector for detecting the magnetic fluxes generated in proximity of the surface of the rotor thereby to determine whether the rotor winding is in fault or not
In these conventional rotor winding fault diagnosis systems, however, a magnetic flux detector is required to be projected into the rotary machine for continuous monitor, and therefore the problem during rotation or heating under high magnetic field is posed, resulting in a low reliability in over long-time operation. In cases other than continuous operation, the magnetic flux detector is inserted into the rotary electric machine while the rotor is rotating, thus giving rise to a danger of contact between the rotor and the magnetic flux detector. Further, in a rotary electric machine of hydrogen-cooling type so constructed that a magnetic flux detector is inserted from outside the machine, the insert ion work is difficult as hydrogen is sealed inside.
In order to solve these problems, rotor winding fault diagnosis system as shown in FIG. 2 has been suggested by one of the inventors of the present invention and another. As shown in FIG. 2, a field winding 1 is supplied with a field current from excitation means 2, and the system further comprises a field current detector 3 and a field voltage detector 4. The field current I detected at the field current detector 3 and the field voltage V detected at the field voltage detector 4 are used to calculate the field resistance R.sub.t =V/I at a given time point t by an arithmetic unit 5. This field resistance R.sub.t is stored in a memory, while a field resistance R.sub.t-.DELTA.t stored a predetermined time .DELTA.t before the ti-e point t is produced from a memory 6, and is compared with the field resistance R.sub.t. If the absolute value if the difference between them is larger than a predetermined value .DELTA.R, a signal is produced as an alarm from a comparator 7. The alarm signal thus produced from the comparator 7 is displayed on a display unit 8.
In this configuration for comparing the field resistance R.sub.t at a given time point t with the field resistance R.sub.t-.DELTA.t at a time point t -.DELTA.t, if a fault such as an inter-layer shorting occurs in the field winding 1 during the time period .DELTA.t, the field resistance R.sub.t-.DELTA.t = 0.5 ohm at a time point t 14 .DELTA.t becomes R.sub.t =0.4 ohm at the time point t, for example. As a result, the absolute value of the difference between the field resistor R.sub.t-.DELTA.t and the field resistance R.sub.t becomes 0.1 ohm. Assume that the value .DELTA.R is set to 0.05 ohm. Then, EQU .vertline.R.sub.t -(R.sub.t -.DELTA.t).vertline.&gt;.DELTA.R ( 1)
An alarm signal is thus produced from the comparator 7, and a fault is indicated on the display unit 8.
If the field winding 1 is disconnected, on the other hand, the field resistance R.sub.t-.DELTA.t at time point t -.DELTA.t becomes R.sub.t =.infin..OMEGA.at time point t. As a consequence, the absolute value of the difference between the two field resistances is .infin..OMEGA.. Therefore, if the value .DELTA.R is set at 0.05 ohm, EQU .vertline.R.sub.t -(R.sub.t -.DELTA.t).vertline.&gt;R ( 2)
The comparator 7 thus produces an alarm signal with a fault indicated on the display unit 8.
In this way, such a fault as an inner-layer shorting or disconnection of the rotor winding is detected by the field current detector 3 and the field voltage detector 4 installed outside of the rotary electric machine on the one hand, and if the value .DELTA.R is set properly, it is possible to diagnose a fault of the rotor winding without being affected by the faulty operation due to noises or the change in field resistance due to temperature increase of the field winding on the other.
The above-described suggested rotor winding fault diagnosis systems in which a fault is detected by the winding resistance of the rotor winding, however, has the disadvantage that if an inter-layer shorting occurs in the rotor winding, for instance, the difference between the winding resistance before and after occurrence of the inter-layer shorting of the rotor winding is very much decreased to an undetectable extent in he case of a great number of turns of the rotor winding involved, so that applications of the diagnosis system are limited.